1. Field of the Invention
This invention relates to fatigue alleviation in aircraft during all phases of the ground-air-ground cycle (GAG).
2. Discussion of Prior Art
This invention relates to fatigue alleviation in aircraft during all phases of the ground-air-ground cycle (GAG).
Due to an increased demand for international air travel and in air traffic generally, there is a recognised need to increase the size and efficiency of both passenger and transporter aircraft. Customers also desire the capability to fly long distances at economical cost. As well as the physical size of the aircraft itself, the engineer has to consider the additional passenger and/or cargo weight to be carried by the craft and the quantity of fuel necessary to take the loaded craft safely to its destination.
A limiting factor in the design of such aircraft is the strength of the materials used, including those of the wing. For all commercial aircraft there are two fundamental design drivers which have to be met. Firstly there are the ultimate load cases; a once-only application of extremely high loading applied during abnormal conditions. There are a large number of these possible conditions and the aircraft is designed to withstand any which are foreseeable and then continue in safe flight and land safely. The aircraft may then be scrapped or require major repair. Secondly during all stages of the ground-air-ground (GAG) cycle, the wing is subjected cyclic loading conditions which cumulatively, over time, lead to the formation and then propagation of micro cracks and may ultimately appear as detectable cracks which require repair or maintenance to the aircraft. During cruise, the wings support the weight of the aircraft and bend upwards, whilst on the ground the wings are supported by the landing gear and possibly fuselage and thus bend downwards. The wings have to be designed to tolerate the damage caused by this cyclic loading to ensure structural integrity for the life of the aircraft. Today's technology allows accurate analysis of the large number of load cases that constitute the ultimate conditions; this allows the conservatisms of yesterdays designs to be reduced, leading to more economic aircraft to operate. The effect of this is that modern aircraft are increasingly defined by the cyclic loading conditions so it is evermore important to find ways to reduce the loading due to the GAG cycle. One approach is to find new ways of using the fuel weight to greater benefit.
Typically large aircraft are equipped with a number of fuel tanks positioned in their wings, the fuselage and tail area. Engine feed tanks are positioned near to the engines ensure a continuous supply of fuel to those engines, other tanks acts as reserves, storing fuel for transfer to the feed tanks as the feed tank supplies are burned. During flight, as the engine feed tanks begin to empty, a control system detects the reduction in fuel level and, once a predetermined level is recorded, causes fuel from the reserve tanks to be transferred to the feed tanks so that there is no interruption in the fuel supply to the engines.
The tankage is the total fuel capacity of the aircraft that is required for the aircraft to achieve its maximum payload range. However a typical flight is much shorter than the maximum so the available fuel tanks are not all filled. This allows a degree of flexibility regarding the positioning of fuel during the flight.
Conventionally, prior to take off, the outermost wing tank is full in anticipation of providing maximum wing bending relief once the aircraft has lifted-off. Unfortunately this also maximises damage to the wing during pre-flight taxiing and the take-off run. This invention seeks to alleviate this problem.
The present invention seeks to alleviate these problems and provide improved fatigue alleviation during the GAG cycle.